This invention deals with curable silicone compositions containing certain silicone resins.
Silicone compositions in general are known for their excellent resistance to environmental stresses, such as low and high temperatures, ultraviolet radiation, and other environmental stresses. Among many such silicone compositions is that disclosed in U.S. Pat. No. 4,322,518,issued Mar. 30, 1982 to John Blizzard, and assigned to the assignee of the present invention. U.S. Pat. No. 4,322,518, discloses a curable silicone composition comprising:
(I) a certain liquid silicone resin; and PA1 (II) a polydiorganosiloxane. PA1 (A) a certain liquid organosilicon resin; PA1 (B) an organosilicon polymer; PA1 (C) an organosilicon resin consisting essentially of Me.sub.2 ViSiO.sub.1/2 units, Me.sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units; and PA1 (D) a hydrosilylation catalyst. PA1 (i) an organosilicon resin consisting essentially of R.sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units wherein R represents a monovalent hydrocarbon radical and the ratio of R.sub.3 SiO.sub.1/2 units to SiO.sub.4/2 units is from 0.6/1 to 0.9/1 and PA1 (ii) a polyorganohydrogensiloxane; PA1 (i) an organosilicon resin consisting essentially of R.sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units in the ratio stated above; and PA1 (ii) a polyorganohydrogensiloxane. PA1 from 1 to 200 parts by weight of Component (A); PA1 100 parts by weight of Component (B); PA1 from 1 to 50 parts by weight of Component (C); and PA1 from 0.00003 to 0.035 parts by weight of Component (D). PA1 from 5 to 100 parts by weight of Component (A), PA1 100 parts by weight of Component (B); PA1 from 5 to 25 parts by weight of Component (C); and PA1 from 0.00014 to 0.025 parts by weight of Component (D). PA1 from 10 to 60 parts by weight of Component (A), 100 parts by weight of Component (B); PA1 from 10 to 25 parts by weight of Component (C); and PA1 from 0.0014 to 0.025 parts by weight of Component (D).
While the curable compositions disclosed in U.S. Pat. No. 4,322,518 represented a significant advance in the art, there remained room for improvement in some of the properties of the cured material. Specifically, there remained room for improvement in the physical strength and the fuel resistance of the cured composition, and in the corrosion protection furnished by the cured composition to a metal substrate coated with that composition.
For the sake of simplicity, the term Me is to be taken as the --CH.sub.3 radical, and the term Vi is to be taken as the --CH=CH.sub.2 radical throughout the following specification.